Outside the nucleus, mesons appear in nature only as short-lived products of very high-energy collisions between particles made of quarks, such as cosmic rays (high-energy protons and neutrons) and ordinary matter. Mesons are also frequently produced artificially in high-energy particle accelerators in the collisions of protons, antiprotons, or other particles.

Mesons are the associated quantum-field particles that transmit the nuclear force between hadrons that pull those together into a nucleus, their effect is analogous to photons that are the force carriers that transmit the electromagnetic force of attraction between oppositely charged protons and electrons that allow individual atoms to exist, and further, to pull atoms together into molecules. Higher energy (more massive) mesons were created momentarily in the Big Bang, but are not thought to play a role in nature today. However, such heavy mesons are regularly created in particle accelerator experiments, in order to understand the nature of the heavier types of quark that compose the heavier mesons.

Mesons are part of the hadron particle family, and are defined simply as particles composed of two quarks, the other members of the hadron family are the baryons: subatomic particles composed of three quarks. Some experiments show evidence of exotic mesons, which do not have the conventional valence quark content of one quark and one antiquark.

Because quarks have a spin of ​1⁄2, the difference in quark number between mesons and baryons results in conventional two-quark mesons being bosons, whereas baryons are fermions.

Each type of meson has a corresponding antiparticle (antimeson) in which quarks are replaced by their corresponding antiquarks and vice versa, for example, a positive pion (π+) is made of one up quark and one down antiquark; and its corresponding antiparticle, the negative pion (π−), is made of one up antiquark and one down quark.

From theoretical considerations, in 1934 Hideki Yukawa[5][6] predicted the existence and the approximate mass of the "meson" as the carrier of the nuclear force that holds atomic nuclei together. If there were no nuclear force, all nuclei with two or more protons would fly apart due to electromagnetic repulsion. Yukawa called his carrier particle the meson, from μέσος mesos, the Greek word for "intermediate", because its predicted mass was between that of the electron and that of the proton, which has about 1,836 times the mass of the electron. Yukawa had originally named his particle the "mesotron", but he was corrected by the physicist Werner Heisenberg (whose father was a professor of Greek at the University of Munich). Heisenberg pointed out that there is no "tr" in the Greek word "mesos".[7]

The first candidate for Yukawa's meson, now known in modern terminology as the muon, was discovered in 1936 by Carl David Anderson and others in the decay products of cosmic ray interactions. The mu meson had about the right mass to be Yukawa's carrier of the strong nuclear force, but over the course of the next decade, it became evident that it was not the right particle, it was eventually found that the "mu meson" did not participate in the strong nuclear interaction at all, but rather behaved like a heavy version of the electron, and was eventually classed as a lepton like the electron, rather than a meson. Physicists in making this choice decided that properties other than particle mass should control their classification.

There were years of delays in the subatomic particle research during World War II (1939–45), with most physicists working in applied projects for wartime necessities. When the war ended in August 1945, many physicists gradually returned to peacetime research, the first true meson to be discovered was what would later be called the "pi meson" (or pion). This discovery was made in 1947, by Cecil Powell, César Lattes, and Giuseppe Occhialini, who were investigating cosmic ray products at the University of Bristol in England, based on photographic films placed in the Andes mountains. Some of those mesons had about the same mass as the already-known meson, yet seemed to decay into it, leading physicist Robert Marshak to hypothesize in 1947 that it was actually a new and different meson, over the next few years, more experiments showed that the pion was indeed involved in strong interactions. The pion (as a virtual particle) is also believed to be the primary force carrier for the nuclear force in atomic nuclei. Other mesons, such as the virtual rho mesons are involved in mediating this force as well, but to a lesser extent. Following the discovery of the pion, Yukawa was awarded the 1949 Nobel Prize in Physics for his predictions.

In the past, the word meson was sometimes used to mean any force carrier, such as the "Z0 meson", which is involved in mediating the weak interaction.[8] However, this spurious usage has fallen out of favor, and mesons are now defined as particles composed of pairs of quarks and antiquarks.

Spin (quantum number S) is a vector quantity that represents the "intrinsic" angular momentum of a particle. It comes in increments of ​1⁄2ħ. The ħ is often dropped because it is the "fundamental" unit of spin, and it is implied that "spin 1" means "spin 1 ħ". (In some systems of natural units, ħ is chosen to be 1, and therefore does not appear in equations.)

Quarks are fermions—specifically in this case, particles having spin ​1⁄2 (S = ​1⁄2). Because spin projections vary in increments of 1 (that is 1 ħ), a single quark has a spin vector of length ​1⁄2, and has two spin projections (Sz = +​1⁄2 and Sz = −​1⁄2). Two quarks can have their spins aligned, in which case the two spin vectors add to make a vector of length S = 1 and three spin projections (Sz = +1, Sz = 0, and Sz = −1), called the spin-1 triplet. If two quarks have unaligned spins, the spin vectors add up to make a vector of length S = 0 and only one spin projection (Sz = 0), called the spin-0 singlet. Because mesons are made of one quark and one antiquark, they can be found in triplet and singlet spin states.

There is another quantity of quantized angular momentum, called the orbital angular momentum (quantum number L), that comes in increments of 1 ħ, which represent the angular momentum due to quarks orbiting around each other. The total angular momentum (quantum number J) of a particle is therefore the combination of intrinsic angular momentum (spin) and orbital angular momentum, it can take any value from J = |L − S| to J = |L + S|, in increments of 1.

Particle physicists are most interested in mesons with no orbital angular momentum (L = 0), therefore the two groups of mesons most studied are the S = 1; L = 0 and S = 0; L = 0, which corresponds to J = 1 and J = 0, although they are not the only ones. It is also possible to obtain J = 1 particles from S = 0 and L = 1. How to distinguish between the S = 1, L = 0 and S = 0, L = 1 mesons is an active area of research in meson spectroscopy.[citation needed]

If the universe were reflected in a mirror, most of the laws of physics would be identical—things would behave the same way regardless of what we call "left" and what we call "right", this concept of mirror reflection is called parity (P). Gravity, the electromagnetic force, and the strong interaction all behave in the same way regardless of whether or not the universe is reflected in a mirror, and thus are said to conserve parity (P-symmetry). However, the weak interaction does distinguish "left" from "right", a phenomenon called parity violation (P-violation).

Based on this, one might think that, if the wavefunction for each particle (more precisely, the quantum field for each particle type) were simultaneously mirror-reversed, then the new set of wavefunctions would perfectly satisfy the laws of physics (apart from the weak interaction). It turns out that this is not quite true: In order for the equations to be satisfied, the wavefunctions of certain types of particles have to be multiplied by −1, in addition to being mirror-reversed, such particle types are said to have negative or odd parity (P = −1, or alternatively P = −), whereas the other particles are said to have positive or even parity (P = +1, or alternatively P = +).

For mesons, the parity is related to the orbital angular momentum by the relation:[9]

P=(−1)L+1{\displaystyle P=\left(-1\right)^{L+1}}

where the L is a result of the parity of the corresponding spherical harmonic of the wavefunction. The "+ 1" comes from the fact that, according to the Dirac equation, a quark and an antiquark have opposite intrinsic parities. Therefore, the intrinsic parity of a meson is the product of the intrinsic parities of the quark (+1) and antiquark (−1), as these are different, their product is −1, and so it contributes the "+ 1" that appears in the exponent.

As a consequence, all mesons with no orbital angular momentum (L = 0) have odd parity (P = −1).

C-parity is only defined for mesons that are their own antiparticle (i.e. neutral mesons). It represents whether or not the wavefunction of the meson remains the same under the interchange of their quark with their antiquark.[10] If

C-parity rarely is studied on its own, but more commonly in combination with P-parity into CP-parity. CP-parity was thought to be conserved, but was later found to be violated in weak interactions.[11][12][13]

G parity is a generalization of the C-parity. Instead of simply comparing the wavefunction after exchanging quarks and antiquarks, it compares the wavefunction after exchanging the meson for the corresponding antimeson, regardless of quark content.[14]

Combinations of one u, d or s quarks and one u, d, or s antiquark in JP = 0− configuration form a nonet.

Combinations of one u, d or s quarks and one u, d, or s antiquark in JP = 1− configuration also form a nonet.

The concept of isospin was first proposed by Werner Heisenberg in 1932 to explain the similarities between protons and neutrons under the strong interaction,[15] although they had different electric charges, their masses were so similar that physicists believed that they were actually the same particle. The different electric charges were explained as being the result of some unknown excitation similar to spin, this unknown excitation was later dubbed isospin by Eugene Wigner in 1937.[16] When the first mesons were discovered, they too were seen through the eyes of isospin and so the three pions were believed to be the same particle, but in different isospin states.

This belief lasted until Murray Gell-Mann proposed the quark model in 1964 (containing originally only the u, d, and s quarks),[17] the success of the isospin model is now understood to be the result of the similar masses of the u and d quarks. Because the u and d quarks have similar masses, particles made of the same number of them also have similar masses, the exact specific u and d quark composition determines the charge, because u quarks carry charge +​2⁄3 whereas d quarks carry charge −​1⁄3. For example, the three pions all have different charges (π+ (ud), π0 (a quantum superposition of uu and dd states), π− (du)), but have similar masses (c. 7002140000000000000♠140 MeV/c2) as they are each made of a same number of total of up and down quarks and antiquarks. Under the isospin model, they were considered to be a single particle in different charged states.

The mathematics of isospin was modeled after that of spin. Isospin projections varied in increments of 1 just like those of spin, and to each projection was associated a "charged state", because the "pion particle" had three "charged states", it was said to be of isospin I = 1. Its "charged states" π+, π0, and π−, corresponded to the isospin projections I3 = +1, I3 = 0, and I3 = −1 respectively. Another example is the "rho particle", also with three charged states, its "charged states" ρ+, ρ0, and ρ−, corresponded to the isospin projections I3 = +1, I3 = 0, and I3 = −1 respectively. It was later noted that the isospin projections were related to the up and down quark content of particles by the relation

In the "isospin picture", the three pions and three rhos were thought to be the different states of two particles. However, in the quark model, the rhos are excited states of pions. Isospin, although conveying an inaccurate picture of things, is still used to classify hadrons, leading to unnatural and often confusing nomenclature, because mesons are hadrons, the isospin classification is also used, with I3 = +​1⁄2 for up quarks and down antiquarks, and I3 = −​1⁄2 for up antiquarks and down quarks.

The strangenessquantum numberS (not to be confused with spin) was noticed to go up and down along with particle mass. The higher the mass, the lower the strangeness (the more s quarks). Particles could be described with isospin projections (related to charge) and strangeness (mass) (see the uds nonet figures), as other quarks were discovered, new quantum numbers were made to have similar description of udc and udb nonets. Because only the u and d mass are similar, this description of particle mass and charge in terms of isospin and flavour quantum numbers only works well for the nonets made of one u, one d and one other quark and breaks down for the other nonets (for example ucb nonet). If the quarks all had the same mass, their behaviour would be called symmetric, because they would all behave in exactly the same way with respect to the strong interaction. However, as quarks do not have the same mass, they do not interact in the same way (exactly like an electron placed in an electric field will accelerate more than a proton placed in the same field because of its lighter mass), and the symmetry is said to be broken.

where S, C, B′, and T represent the strangeness, charm, bottomness and topness flavour quantum numbers respectively. They are related to the number of strange, charm, bottom, and top quarks and antiquark according to the relations:

S=−(ns−ns¯){\displaystyle S=-(n_{s}-n_{\bar {s}})}

C=+(nc−nc¯){\displaystyle C=+(n_{c}-n_{\bar {c}})}

B′=−(nb−nb¯){\displaystyle B^{\prime }=-(n_{b}-n_{\bar {b}})}

T=+(nt−nt¯),{\displaystyle T=+(n_{t}-n_{\bar {t}}),}

meaning that the Gell-Mann–Nishijima formula is equivalent to the expression of charge in terms of quark content:

Flavoured mesons are mesons made of pair of quark and antiquarks of different flavours, the rules are simpler in this case: the main symbol depends on the heavier quark, the superscript depends on the charge, and the subscript (if any) depends on the lighter quark. In table form, they are:[19]

There is experimental evidence for particles that are hadrons (i.e., are composed of quarks) and are color-neutral with zero baryon number, and thus by conventional definition are mesons. Yet, these particles do not consist of a single quark/antiquark pair, as all the other conventional mesons discussed above do. A tentative category for these particles is exotic mesons.

There are at least five exotic meson resonances that have been experimentally confirmed to exist by two or more independent experiments, the most statistically significant of these is the Z(4430), discovered by the Belle experiment in 2007 and confirmed by LHCb in 2014. It is a candidate for being a tetraquark: a particle composed of two quarks and two antiquarks.[22] See the main article above for other particle resonances that are candidates for being exotic mesons.

^ abcFor the purpose of nomenclature, the isospin projection I3 isn't considered a flavour quantum number. This means that the charged pion-like mesons (π±, a±, b±, and ρ± mesons) follow the rules of flavourless mesons, even if they aren't truly "flavourless".

1.
Particle
–
A particle is a minute fragment or quantity of matter. In the physical sciences, a particle is a small localized object to which can be ascribed several physical or chemical properties such as volume or mass. Particles can also be used to create models of even larger objects depending on their density. The term particle is rather general in meaning, and is refined as needed by various scientific fields, something that is composed of particles may be referred to as being particulate. However, the particulate is most frequently used to refer to pollutants in the Earths atmosphere. The concept of particles is particularly useful when modelling nature, as the treatment of many phenomena can be complex. It can be used to make simplifying assumptions concerning the processes involved, francis Sears and Mark Zemansky, in University Physics, give the example of calculating the landing location and speed of a baseball thrown in the air. The treatment of large numbers of particles is the realm of statistical physics, the term particle is usually applied differently to three classes of sizes. The term macroscopic particle, usually refers to particles much larger than atoms and these are usually abstracted as point-like particles, or even invisible. This is even though they have volumes, shapes, structures, examples of macroscopic particles would include powder, dust, sand, pieces of debris during a car accident, or even objects as big as the stars of a galaxy. Another type, microscopic particles usually refers to particles of sizes ranging from atoms to molecules, such as carbon dioxide, nanoparticles and these particles are studied in chemistry, as well as atomic and molecular physics. The smallest of particles are the particles, which refer to particles smaller than atoms. These particles are studied in particle physics, because of their extremely small size, the study of microscopic and subatomic particles fall in the realm of quantum mechanics. Particles can also be classified according to composition, composite particles refer to particles that have composition – that is particles which are made of other particles. For example, an atom is made of six protons, eight neutrons. By contrast, elementary particles refer to particles that are not made of other particles, according to our current understanding of the world, only a very small number of these exist, such as the leptons, quarks or gluons. However it is possible some of these might turn up to be composite particles after all. While composite particles can very often be considered point-like, elementary particles are truly punctual, both elementary and composite particles, are known to undergo particle decay

2.
Composite particle
–
This article includes a list of the different types of atomic- and sub-atomic particles found or believed to exist in the whole of the universe. For individual lists of the different particles, see the list below, Elementary particles are particles with no measurable internal structure, that is, they are not composed of other particles. They are the objects of quantum field theory. Many families and sub-families of elementary particles exist, Elementary particles are classified according to their spin. Fermions have half-integer spin while bosons have integer spin, all the particles of the Standard Model have been experimentally observed, recently including the Higgs boson. Fermions are one of the two classes of particles, the other being bosons. Fermion particles are described by Fermi–Dirac statistics and have quantum numbers described by the Pauli exclusion principle and they include the quarks and leptons, as well as any composite particles consisting of an odd number of these, such as all baryons and many atoms and nuclei. Fermions have half-integer spin, for all known elementary fermions this is 1⁄2, all known fermions, except neutrinos, are also Dirac fermions, that is, each known fermion has its own distinct antiparticle. It is not known whether the neutrino is a Dirac fermion or a Majorana fermion, fermions are the basic building blocks of all matter. They are classified according to whether they interact via the force or not. In the Standard Model, there are 12 types of fermions, six quarks. Quarks are the constituents of hadrons and interact via the strong interaction. Quarks are the only carriers of fractional charge, but because they combine in groups of three or in pairs of one quark and one antiquark, only integer charge is observed in nature. Their respective antiparticles are the antiquarks, which are identical except that they carry the electric charge, color charge. There are six flavors of quarks, the three positively charged quarks are called up-type quarks and the three negatively charged quarks are called down-type quarks, leptons do not interact via the strong interaction. Their respective antiparticles are the antileptons which are identical, except for the fact that they carry the electric charge. The antiparticle of an electron is an antielectron, which is always called a positron for historical reasons. There are six leptons in total, the three charged leptons are called leptons, while the neutral leptons are called neutrinos

3.
Quark
–
A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, due to a phenomenon known as color confinement, quarks are never directly observed or found in isolation, they can be found only within hadrons, such as baryons and mesons. For this reason, much of what is known about quarks has been drawn from observations of the hadrons themselves, Quarks have various intrinsic properties, including electric charge, mass, color charge, and spin. There are six types of quarks, known as flavors, up, down, strange, charm, top, up and down quarks have the lowest masses of all quarks. The heavier quarks rapidly change into up and down quarks through a process of particle decay, the transformation from a higher mass state to a lower mass state. Because of this, up and down quarks are generally stable and the most common in the universe, whereas strange, charm, bottom, and top quarks can only be produced in high energy collisions. For every quark flavor there is a type of antiparticle, known as an antiquark. The quark model was proposed by physicists Murray Gell-Mann and George Zweig in 1964. Accelerator experiments have provided evidence for all six flavors, the top quark was the last to be discovered at Fermilab in 1995. The Standard Model is the theoretical framework describing all the known elementary particles. This model contains six flavors of quarks, named up, down, strange, charm, bottom, antiparticles of quarks are called antiquarks, and are denoted by a bar over the symbol for the corresponding quark, such as u for an up antiquark. As with antimatter in general, antiquarks have the mass, mean lifetime, and spin as their respective quarks. Quarks are spin- 1⁄2 particles, implying that they are fermions according to the spin-statistics theorem and they are subject to the Pauli exclusion principle, which states that no two identical fermions can simultaneously occupy the same quantum state. This is in contrast to bosons, any number of which can be in the same state, unlike leptons, quarks possess color charge, which causes them to engage in the strong interaction. The resulting attraction between different quarks causes the formation of composite particles known as hadrons, there are two families of hadrons, baryons, with three valence quarks, and mesons, with a valence quark and an antiquark. The most common baryons are the proton and the neutron, the blocks of the atomic nucleus. A great number of hadrons are known, most of them differentiated by their quark content, the existence of exotic hadrons with more valence quarks, such as tetraquarks and pentaquarks, has been conjectured but not proven. However, on 13 July 2015, the LHCb collaboration at CERN reported results consistent with pentaquark states, elementary fermions are grouped into three generations, each comprising two leptons and two quarks

4.
Antiparticle
–
Corresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite charge. For example, the antiparticle of the electron is the positron, the opposite is also true, the antiparticle of the positron is the electron. Some particles, such as the photon, are their own antiparticle, otherwise, for each pair of antiparticle partners, one is designated as normal matter, and the other as antimatter. Particle–antiparticle pairs can annihilate each other, producing photons, since the charges of the particle and antiparticle are opposite, for example, the positrons produced in natural radioactive decay quickly annihilate themselves with electrons, producing pairs of gamma rays, a process exploited in positron emission tomography. The laws of nature are very nearly symmetrical with respect to particles and antiparticles, for example, an antiproton and a positron can form an antihydrogen atom, which is believed to have the same properties as a hydrogen atom. The discovery of Charge Parity violation helped to shed light on this problem by showing that this symmetry, antiparticles are produced naturally in beta decay, and in the interaction of cosmic rays in the Earths atmosphere. Because charge is conserved, it is not possible to create an antiparticle without either destroying a particle of the charge or by creating a particle of the opposite charge. The latter is seen in many processes in both a particle and its antiparticle are created simultaneously, as in particle accelerators. This is the inverse of the annihilation process. Although particles and their antiparticles have opposite charges, electrically neutral particles need not be identical to their antiparticles. The neutron, for example, is out of quarks, the antineutron from antiquarks. However, other particles are their own antiparticles, such as photons, hypothetical gravitons. The electric charge-to-mass ratio of a particle can be measured by observing the radius of curling of its track in a magnetic field. Positrons, because of the direction that their paths curled, were at first mistaken for electrons travelling in the opposite direction, the antiproton and antineutron were found by Emilio Segrè and Owen Chamberlain in 1955 at the University of California, Berkeley. Since then, the antiparticles of many subatomic particles have been created in particle accelerator experiments. In recent years, complete atoms of antimatter have been assembled out of antiprotons and positrons, solutions of the Dirac equation contained negative energy quantum states. As a result, an electron could always radiate energy and fall into an energy state. Even worse, it could keep radiating infinite amounts of energy because there were many negative energy states available

5.
Particle statistics
–
Particle statistics is a particular description of multiple particles in statistical mechanics. Its core concept is an ensemble that emphasizes properties of a large system as a whole at the expense of knowledge about parameters of separate particles. When an ensemble consists of particles with similar properties, their number is called the particle number, in classical mechanics, all particles in the system are considered distinguishable. This means that particles in a system can be tracked. As a consequence, changing the position of any two particles in the leads to a completely different configuration of the entire system. Furthermore, there is no restriction on placing more than one particle in any given state accessible to the system and these characteristics of classical positions are called Maxwell–Boltzmann statistics. The fundamental feature of quantum mechanics that distinguishes it from classical mechanics is that particles of a type are indistinguishable from one another. This means that in an assembly consisting of particles, interchanging any two particles does not lead to a new configuration of the system. In the case of a system consisting of particles of different kinds, all quantum particles, such as leptons and baryons, in the universe have three translational motion degrees of freedom and one discrete degree of freedom, known as spin. Thats why quantum statistics is useful when one considers, say, helium liquid or ammonia gas, the spin–statistics theorem binds two particular kinds of combinatorial symmetry with two particular kinds of spin symmetry, namely bosons and fermions. In Bose–Einstein statistics interchanging any two particles of the leaves the resultant system in a symmetric state. That is, the function of the system before interchanging equals the wave function of the system after interchanging. It is important to emphasize that the function of the system has not changed itself. This has very important consequences on the state of the system and it is found that the particles that obey Bose–Einstein statistics are the ones which have integer spins, which are therefore called bosons. Examples of bosons include photons and helium-4, one type of system obeying B–E statistics is the Bose–Einstein condensate where all particles of the assembly exist in the same state. In Fermi–Dirac statistics interchanging any two particles of the leaves the resultant system in an antisymmetric state. That is, the function of the system before interchanging is the wave function of the system after interchanging. Again, the function of the system itself does not change

6.
Boson
–
In quantum mechanics, a boson is a particle that follows Bose–Einstein statistics. Bosons make up one of the two classes of particles, the other being fermions, an important characteristic of bosons is that their statistics do not restrict the number of them that occupy the same quantum state. This property is exemplified by helium-4 when it is cooled to become a superfluid, unlike bosons, two identical fermions cannot occupy the same quantum space. Whereas the elementary particles that make up matter are fermions, the elementary bosons are force carriers that function as the glue holding matter together and this property holds for all particles with integer spin as a consequence of the spin–statistics theorem. This state is called Bose-Einstein condensation and it is believed that this property is the explanation of superfluidity. Bosons may be elementary, like photons, or composite. If it exists, a graviton must be a boson, composite bosons are important in superfluidity and other applications of Bose–Einstein condensates. This phenomenon is known as Bose-Einstein condensation and it is believed that this phenomenon is the secret behind superfluidity of liquids, Bosons differ from fermions, which obey Fermi–Dirac statistics. Two or more identical fermions cannot occupy the same quantum state, since bosons with the same energy can occupy the same place in space, bosons are often force carrier particles. Fermions are usually associated with matter Bosons are particles which obey Bose–Einstein statistics, thus fermions are sometimes said to be the constituents of matter, while bosons are said to be the particles that transmit interactions, or the constituents of radiation. The quantum fields of bosons are bosonic fields, obeying canonical commutation relations, the properties of lasers and masers, superfluid helium-4 and Bose–Einstein condensates are all consequences of statistics of bosons. Interactions between elementary particles are called fundamental interactions, the fundamental interactions of virtual bosons with real particles result in all forces we know. All known elementary and composite particles are bosons or fermions, depending on their spin, particles with spin are fermions. In the framework of quantum mechanics, this is a purely empirical observation. However, in quantum field theory, the spin–statistics theorem shows that half-integer spin particles cannot be bosons. In large systems, the difference between bosonic and fermionic statistics is only apparent at large densities—when their wave functions overlap, at low densities, both types of statistics are well approximated by Maxwell–Boltzmann statistics, which is described by classical mechanics. All observed elementary particles are fermions or bosons. The observed elementary bosons are all bosons, photons, W and Z bosons, gluons

7.
Fundamental interaction
–
In physics, the fundamental interactions, also known as fundamental forces, are the interactions that do not appear to be reducible to more basic interactions. There are four conventionally accepted fundamental interactions—gravitational, electromagnetic, strong, each one is described mathematically as a field. The gravitational force is modelled as a classical field. The other three, part of the Standard Model of particle physics, are described as discrete quantum fields, and their interactions are carried by a quantum. The strong and weak interactions have short ranges, producing forces at minuscule, subatomic distances, the strong interaction, which is carried by the gluon particle, is responsible for the binding of quarks together to form hadrons, such as protons and neutrons. As a residual effect, it creates the force that binds the latter particles to form atomic nuclei. The weak interaction, which is carried by the W and Z particles, also acts on the nucleus, the other two, electromagnetism and gravity, produce significant forces at macroscopic scales where the effects can be seen directly in everyday life. The electromagnetic force, carried by the photon, creates electric and magnetic fields, Electromagnetic forces tend to cancel each other out when large collections of objects are considered, so over the largest distances, gravity tends to be the dominant force. Other theorists seek to unite the electroweak and strong fields within a Grand Unified Theory, some theories, notably string theory, seek both QG and GUT within one framework, unifying all four fundamental interactions along with mass generation within a theory of everything. A few researchers have interpreted various anomalous observations in physics as evidence for a fifth force, inferring that all objects bearing mass approach at a constant rate, but collide by impact proportional to their masses, Newton inferred that matter exhibits an attractive force. Thus Newtons theory violated the first principle of mechanical philosophy, as stated by Descartes, conversely, during the 1820s, when explaining magnetism, Michael Faraday inferred a field filling space and transmitting that force. Faraday conjectured that ultimately, all unified into one. In the early 1870s, James Clerk Maxwell unified electricity and magnetism as effects of a field whose third consequence was light. The Standard Model of particle physics was developed throughout the half of the 20th century. In the Standard Model, the electromagnetic, strong, and weak interactions associate with elementary particles, for predictive success with QMs probabilistic outcomes, particle physics conventionally models QM events across a field set to special relativity, altogether relativistic quantum field theory. Force particles, called gauge bosons—force carriers or messenger particles of underlying fields—interact with matter particles, everyday matter is atoms, composed of three fermion types, up-quarks and down-quarks constituting, as well as electrons orbiting, the atoms nucleus. The electromagnetic interaction was modelled with the interaction, whose force carriers are W and Z bosons, traversing the minuscule distance. Electroweak interaction would operate at high temperatures as soon after the presumed Big Bang

8.
Strong interaction
–
At the range of 10−15 m, the strong force is approximately 137 times as strong as electromagnetism, a million times as strong as the weak interaction and 1038 times as strong as gravitation. The strong nuclear force holds most ordinary matter together because it confines quarks into hadron particles such as proton and neutron, in addition, the strong force binds neutrons and protons to create atomic nuclei. Most of the mass of a proton or neutron is the result of the strong force field energy. The strong interaction is observable at two ranges, on a scale, it is the force that binds protons and neutrons together to form the nucleus of an atom. On the smaller scale, it is the force that holds together to form protons, neutrons. In the latter context, it is known as the color force. The strong force inherently has such a strength that hadrons bound by the strong force can produce new massive particles. Thus, if hadrons are struck by particles, they give rise to new hadrons instead of emitting freely moving radiation. This property of the force is called color confinement, and it prevents the free emission of the strong force, instead, in practice. In the context of binding protons and neutrons together to form atomic nuclei, in this case, it is the residuum of the strong interaction between the quarks that make up the protons and neutrons. As such, the strong interaction obeys a quite different distance-dependent behavior between nucleons, from when it is acting to bind quarks within nucleons. The binding energy that is released on the breakup of a nucleus is related to the residual strong force and is harnessed as fission energy in nuclear power. The strong interaction is mediated by the exchange of particles called gluons that act between quarks, antiquarks, and other gluons. Gluons are thought to interact with quarks and other gluons by way of a type of charge called color charge. Color charge is analogous to electromagnetic charge, but it comes in three rather than one, which results in a different type of force, with different rules of behavior. These rules are detailed in the theory of quantum chromodynamics, which is the theory of quark-gluon interactions, after the Big Bang and during the electroweak epoch of the universe, the electroweak force separated from the strong force. A Grand Unified Theory is hypothesized to exist to describe this, but no theory has yet been successfully formulated. Before the 1970s, physicists were uncertain as to how the nucleus was bound together

9.
Weak interaction
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In particle physics, the weak interaction is one of the four known fundamental interactions of nature, alongside the strong interaction, electromagnetism, and gravitation. The weak interaction is responsible for radioactive decay, which plays an role in nuclear fission. The theory of the interaction is sometimes called quantum flavourdynamics, in analogy with the terms QCD dealing with the strong interaction. However the term QFD is rarely used because the force is best understood in terms of electro-weak theory. The Standard Model of particle physics, which does not address gravity, provides a framework for understanding how the electromagnetic, weak. An interaction occurs when two particles, typically but not necessarily half-integer spin fermions, exchange integer-spin, force-carrying bosons, the fermions involved in such exchanges can be either elementary or composite, although at the deepest levels, all weak interactions ultimately are between elementary particles. In the case of the interaction, fermions can exchange three distinct types of force carriers known as the W+, W−, and Z bosons. The mass of each of these bosons is far greater than the mass of a proton or neutron, the force is in fact termed weak because its field strength over a given distance is typically several orders of magnitude less than that of the strong nuclear force or electromagnetic force. During the quark epoch of the universe, the electroweak force separated into the electromagnetic. Important examples of the weak interaction include beta decay, and the fusion of hydrogen into deuterium that powers the Suns thermonuclear process, most fermions will decay by a weak interaction over time. Such decay makes radiocarbon dating possible, as carbon-14 decays through the interaction to nitrogen-14. It can also create radioluminescence, commonly used in tritium illumination, quarks, which make up composite particles like neutrons and protons, come in six flavours – up, down, strange, charm, top and bottom – which give those composite particles their properties. The weak interaction is unique in that it allows for quarks to swap their flavour for another, the swapping of those properties is mediated by the force carrier bosons. Also, the interaction is the only fundamental interaction that breaks parity-symmetry, and similarly. In 1933, Enrico Fermi proposed the first theory of the weak interaction and he suggested that beta decay could be explained by a four-fermion interaction, involving a contact force with no range. However, it is described as a non-contact force field having a finite range. The existence of the W and Z bosons was not directly confirmed until 1983, the weak interaction is unique in a number of respects, It is the only interaction capable of changing the flavour of quarks. It is the interaction that violates P or parity-symmetry

10.
Electromagnetism
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Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force usually exhibits electromagnetic fields such as fields, magnetic fields. The other three fundamental interactions are the interaction, the weak interaction, and gravitation. The word electromagnetism is a form of two Greek terms, ἤλεκτρον, ēlektron, amber, and μαγνῆτις λίθος magnētis lithos, which means magnesian stone. The electromagnetic force plays a role in determining the internal properties of most objects encountered in daily life. Ordinary matter takes its form as a result of forces between individual atoms and molecules in matter, and is a manifestation of the electromagnetic force. Electrons are bound by the force to atomic nuclei, and their orbital shapes. The electromagnetic force governs the processes involved in chemistry, which arise from interactions between the electrons of neighboring atoms, there are numerous mathematical descriptions of the electromagnetic field. In classical electrodynamics, electric fields are described as electric potential, although electromagnetism is considered one of the four fundamental forces, at high energy the weak force and electromagnetic force are unified as a single electroweak force. In the history of the universe, during the epoch the unified force broke into the two separate forces as the universe cooled. Originally, electricity and magnetism were considered to be two separate forces, Magnetic poles attract or repel one another in a manner similar to positive and negative charges and always exist as pairs, every north pole is yoked to a south pole. An electric current inside a wire creates a corresponding magnetic field outside the wire. Its direction depends on the direction of the current in the wire. A current is induced in a loop of wire when it is moved toward or away from a field, or a magnet is moved towards or away from it. While preparing for a lecture on 21 April 1820, Hans Christian Ørsted made a surprising observation. As he was setting up his materials, he noticed a compass needle deflected away from north when the electric current from the battery he was using was switched on. At the time of discovery, Ørsted did not suggest any explanation of the phenomenon. However, three later he began more intensive investigations

11.
Gravity
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Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward one another, including planets, stars and galaxies. Since energy and mass are equivalent, all forms of energy, including light, on Earth, gravity gives weight to physical objects and causes the ocean tides. Gravity has a range, although its effects become increasingly weaker on farther objects. The most extreme example of this curvature of spacetime is a hole, from which nothing can escape once past its event horizon. More gravity results in time dilation, where time lapses more slowly at a lower gravitational potential. Gravity is the weakest of the four fundamental interactions of nature, the gravitational attraction is approximately 1038 times weaker than the strong force,1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, gravity has an influence on the behavior of subatomic particles. On the other hand, gravity is the dominant interaction at the macroscopic scale, for this reason, in part, pursuit of a theory of everything, the merging of the general theory of relativity and quantum mechanics into quantum gravity, has become an area of research. While the modern European thinkers are credited with development of gravitational theory, some of the earliest descriptions came from early mathematician-astronomers, such as Aryabhata, who had identified the force of gravity to explain why objects do not fall out when the Earth rotates. Later, the works of Brahmagupta referred to the presence of force, described it as an attractive force. Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and this was a major departure from Aristotles belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass may fall slower in an atmosphere, galileos work set the stage for the formulation of Newtons theory of gravity. In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newtons theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the position of the planet. A discrepancy in Mercurys orbit pointed out flaws in Newtons theory, the issue was resolved in 1915 by Albert Einsteins new theory of general relativity, which accounted for the small discrepancy in Mercurys orbit. The simplest way to test the equivalence principle is to drop two objects of different masses or compositions in a vacuum and see whether they hit the ground at the same time. Such experiments demonstrate that all objects fall at the rate when other forces are negligible

12.
Hideki Yukawa
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Hideki Yukawa ForMemRS FRSE, was a Japanese theoretical physicist and the first Japanese Nobel laureate. He was born as Hideki Ogawa in Tokyo and grew up in Kyoto with two brothers, two older sisters, and two younger brothers. He read the Confucian Doctrine of the Mean, and later Lao-Tzu and Chuang-Tzu and his father, for a time, considered sending him to technical college rather than university since he was not as outstanding a student as his older brothers. Ogawa decided against becoming a mathematician when in school, his teacher marked his exam answer as incorrect when Ogawa proved a theorem. He decided against a career in physics in college when he demonstrated clumsiness in glassblowing. In 1929, after receiving his degree from Kyoto Imperial University, after graduation, he was interested in theoretical physics, particularly in the theory of elementary particles. In 1932, he married Sumi Yukawa, the couple had two sons, Harumi and Takaaki. In 1933 he became an assistant professor at, at 26 years old, in 1935 he published his theory of mesons, which explained the interaction between protons and neutrons, and was a major influence on research into elementary particles. In 1940 he became a professor in Kyoto University, in 1940 he won the Imperial Prize of the Japan Academy, in 1943 the Decoration of Cultural Merit from the Japanese government. Yukawa also worked on the theory of K-capture, in which a low energy electron is absorbed by the nucleus, Yukawa became the first chairman of Yukawa Institute for Theoretical Physics in 1953. He was an editor of Progress of Theoretical Physics, and published the books Introduction to Quantum Mechanics, in 1955, he joined ten other leading scientists and intellectuals in signing the Russell–Einstein Manifesto, calling for nuclear disarmament. Yukawa retired from Kyoto University in 1970 as a Professor Emeritus, owing to increasing infirmity, in his final years he appeared in public in a wheelchair. He died at his home in Sakyo-ku, Kyoto, on 8 September 1981 from pneumonia and heart failure and his tomb is in Higashiyama-ku, Kyoto. Solo violinist Diana Yukawa is a relative of Hideki Yukawa

13.
Invariant mass
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More precisely, it is a characteristic of the systems total energy and momentum that is the same in all frames of reference related by Lorentz transformations. If a center of momentum frame exists for the system, then the invariant mass of a system is equal to its mass in that rest frame. In other reference frames, where the momentum is nonzero, the total mass of the system is greater than the invariant mass. Due to mass-energy equivalence, the rest energy of the system is simply the invariant mass times the speed of light squared, similarly, the total energy of the system is its total mass times the speed of light squared. Systems whose four-momentum is a null vector have zero invariant mass, a physical object or particle moving faster than the speed of light would have space-like four-momenta, and these do not appear to exist. Any time-like four-momentum possesses a frame where the momentum is zero. In this case, invariant mass is positive and is referred to as the rest mass, if objects within a system are in relative motion, then the invariant mass of the whole system will differ from the sum of the objects rest masses. This is also equal to the energy of the system divided by c2. See mass–energy equivalence for a discussion of definitions of mass, for example, a scale would measure the kinetic energy of the molecules in a bottle of gas to be part of invariant mass of the bottle, and thus also its rest mass. The same is true for massless particles in such system, which add invariant mass and also rest mass to systems, for an isolated massive system, the center of mass of the system moves in a straight line with a steady sub-luminal velocity. Thus, an observer can always be placed to move along with it. In this frame, which is the center of momentum frame, the momentum is zero. In this frame, which exists under these assumptions, the invariant mass of the system is equal to the system energy divided by c2. This total energy in the center of momentum frame, is the energy which the system may be observed to have. Note that for reasons above, such a rest frame does not exist for single photons, when two or more photons move in different directions, however, a center of mass frame exists. Thus, the mass of a system of several photons moving in different directions is positive, for example, rest mass and invariant mass are zero for individual photons even though they may add mass to the invariant mass of systems. For this reason, invariant mass is in not an additive quantity. Consider the simple case of system, where object A is moving towards another object B which is initially at rest

14.
Pion
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In particle physics, a pion is any of three subatomic particles, π0, π+, and π−. Each pion consists of a quark and an antiquark and is therefore a meson, pions are the lightest mesons, because they are composed of the lightest quarks. They are unstable, with the charged pions π+ and π− decaying with a lifetime of 26 nanoseconds. Charged pions most often decay into muons and muon neutrinos, while neutral pions decay into gamma rays. The exchange of virtual pions, along with the vector, rho and omega mesons, pions are not produced in radioactive decay, but are commonly produced in high energy accelerators in collisions between hadrons. All types of pions are produced in natural processes when high energy cosmic ray protons. The concept of mesons as the particles of the nuclear force was first proposed in 1935 by Hideki Yukawa. While the muon was first proposed to be this particle after its discovery in 1936, the pions, which turned out to be examples of Yukawas proposed mesons, were discovered later, the charged pions in 1947, and the neutral pion in 1950. Theoretical work by Hideki Yukawa in 1935 had predicted the existence of mesons as the particles of the strong nuclear force. From the range of the nuclear force, Yukawa predicted the existence of a particle having a mass of about 100 MeV. Initially after its discovery in 1936, the muon was thought to be this particle, however, later experiments showed that the muon did not participate in the strong nuclear interaction. In modern terminology, this makes the muon a lepton, however, some communities of astrophysicists continue to call the muon a mu-meson. In 1947, the first true mesons, the pions, were found by the collaboration of Cecil Powell, César Lattes, Giuseppe Occhialini, et al. at the University of Bristol. Since the advent of particle accelerators had not yet come, high-energy subatomic particles were only obtainable from atmospheric cosmic rays, after the development of the photographic plates, microscopic inspection of the emulsions revealed the tracks of charged subatomic particles. Pions were first identified by their unusual double meson tracks, which were left by their decay into a putative meson, the particle was identified as a muon, which is not typically classified as a meson in modern particle physics. Further advanced theoretical work was carried out by Riazuddin, who in 1959, since the neutral pion is not electrically charged, it is more difficult to detect and observe than the charged pions are. Neutral pions do not leave tracks in photographic emulsions, and neither do they in Wilson cloud chambers, the existence of the neutral pion was inferred from observing its decay products from cosmic rays, a so-called soft component of slow electrons with photons. The π0 was identified definitively at the University of Californias cyclotron in 1950 by observing its decay into two photons, later in the same year, they were also observed in cosmic-ray balloon experiments at Bristol University

15.
Upsilon meson
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The Upsilon meson is a quarkonium state formed from a bottom quark and its antiparticle. It has a lifetime of 1. 21×10−20 s and a mass about 9.46 GeV/c2 in the ground state, oops-Leon, an erroneously-claimed discovery of a similar particle at a lower mass in 1976. The ϕ particle is the state made from strange quarks. The J/ψ particle is the state made from charm quarks. Observation of a Dimuon Resonance at 9.5 Gev in 400-GeV Proton-Nucleus Collisions, the Discovery of the b Quark at Fermilab in 1977, The Experiment Coordinators Story. Review of Particle Physics – ϒ meson

16.
Electric charge
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Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of charges, positive and negative. Like charges repel and unlike attract, an absence of net charge is referred to as neutral. An object is charged if it has an excess of electrons. The SI derived unit of charge is the coulomb. In electrical engineering, it is common to use the ampere-hour. The symbol Q often denotes charge, early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that dont require consideration of quantum effects. The electric charge is a conserved property of some subatomic particles. Electrically charged matter is influenced by, and produces, electromagnetic fields, the interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the four fundamental forces. 602×10−19 coulombs. The proton has a charge of +e, and the electron has a charge of −e, the study of charged particles, and how their interactions are mediated by photons, is called quantum electrodynamics. Charge is the property of forms of matter that exhibit electrostatic attraction or repulsion in the presence of other matter. Electric charge is a property of many subatomic particles. The charges of free-standing particles are integer multiples of the charge e. Michael Faraday, in his electrolysis experiments, was the first to note the discrete nature of electric charge, robert Millikans oil drop experiment demonstrated this fact directly, and measured the elementary charge. By convention, the charge of an electron is −1, while that of a proton is +1, charged particles whose charges have the same sign repel one another, and particles whose charges have different signs attract. The charge of an antiparticle equals that of the corresponding particle, quarks have fractional charges of either −1/3 or +2/3, but free-standing quarks have never been observed. The electric charge of an object is the sum of the electric charges of the particles that make it up. An ion is an atom that has lost one or more electrons, giving it a net charge, or that has gained one or more electrons

17.
Spin (physics)
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In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles, and atomic nuclei. Spin is one of two types of angular momentum in mechanics, the other being orbital angular momentum. In some ways, spin is like a vector quantity, it has a definite magnitude, all elementary particles of a given kind have the same magnitude of spin angular momentum, which is indicated by assigning the particle a spin quantum number. The SI unit of spin is the or, just as with classical angular momentum, very often, the spin quantum number is simply called spin leaving its meaning as the unitless spin quantum number to be inferred from context. When combined with the theorem, the spin of electrons results in the Pauli exclusion principle. Wolfgang Pauli was the first to propose the concept of spin, in 1925, Ralph Kronig, George Uhlenbeck and Samuel Goudsmit at Leiden University suggested an physical interpretation of particles spinning around their own axis. The mathematical theory was worked out in depth by Pauli in 1927, when Paul Dirac derived his relativistic quantum mechanics in 1928, electron spin was an essential part of it. As the name suggests, spin was originally conceived as the rotation of a particle around some axis and this picture is correct so far as spin obeys the same mathematical laws as quantized angular momenta do. On the other hand, spin has some properties that distinguish it from orbital angular momenta. Although the direction of its spin can be changed, a particle cannot be made to spin faster or slower. The spin of a particle is associated with a magnetic dipole moment with a g-factor differing from 1. This could only occur if the internal charge of the particle were distributed differently from its mass. The conventional definition of the quantum number, s, is s = n/2. Hence the allowed values of s are 0, 1/2,1, 3/2,2, the value of s for an elementary particle depends only on the type of particle, and cannot be altered in any known way. The spin angular momentum, S, of any system is quantized. The allowed values of S are S = ℏ s = h 4 π n, in contrast, orbital angular momentum can only take on integer values of s, i. e. even-numbered values of n. Those particles with half-integer spins, such as 1/2, 3/2, 5/2, are known as fermions, while particles with integer spins. The two families of particles obey different rules and broadly have different roles in the world around us, a key distinction between the two families is that fermions obey the Pauli exclusion principle, that is, there cannot be two identical fermions simultaneously having the same quantum numbers

18.
Particle physics
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Particle physics is the branch of physics that studies the nature of the particles that constitute matter and radiation. By our current understanding, these particles are excitations of the quantum fields that also govern their interactions. The currently dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model, in more technical terms, they are described by quantum state vectors in a Hilbert space, which is also treated in quantum field theory. All particles and their interactions observed to date can be described almost entirely by a field theory called the Standard Model. The Standard Model, as formulated, has 61 elementary particles. Those elementary particles can combine to form composite particles, accounting for the hundreds of species of particles that have been discovered since the 1960s. The Standard Model has been found to agree with almost all the tests conducted to date. However, most particle physicists believe that it is a description of nature. In recent years, measurements of mass have provided the first experimental deviations from the Standard Model. The idea that all matter is composed of elementary particles dates from at least the 6th century BC, in the 19th century, John Dalton, through his work on stoichiometry, concluded that each element of nature was composed of a single, unique type of particle. Throughout the 1950s and 1960s, a variety of particles were found in collisions of particles from increasingly high-energy beams. It was referred to informally as the particle zoo, the current state of the classification of all elementary particles is explained by the Standard Model. It describes the strong, weak, and electromagnetic fundamental interactions, the species of gauge bosons are the gluons, W−, W+ and Z bosons, and the photons. The Standard Model also contains 24 fundamental particles, which are the constituents of all matter, finally, the Standard Model also predicted the existence of a type of boson known as the Higgs boson. Early in the morning on 4 July 2012, physicists with the Large Hadron Collider at CERN announced they had found a new particle that behaves similarly to what is expected from the Higgs boson, the worlds major particle physics laboratories are, Brookhaven National Laboratory. Its main facility is the Relativistic Heavy Ion Collider, which collides heavy ions such as gold ions and it is the worlds first heavy ion collider, and the worlds only polarized proton collider. Its main projects are now the electron-positron colliders VEPP-2000, operated since 2006 and its main project is now the Large Hadron Collider, which had its first beam circulation on 10 September 2008, and is now the worlds most energetic collider of protons. It also became the most energetic collider of heavy ions after it began colliding lead ions and its main facility is the Hadron Elektron Ring Anlage, which collides electrons and positrons with protons

19.
Hadron
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In particle physics, a hadron /ˈhædrɒn/ is a composite particle made of quarks held together by the strong force in a similar way as molecules are held together by the electromagnetic force. Hadrons are categorized into two families, baryons, made of three quarks, and mesons, made of one quark and one antiquark, protons and neutrons are examples of baryons, pions are an example of a meson. Hadrons containing more than three valence quarks have been discovered in recent years, a tetraquark state, named the Z−, was discovered in 2007 by the Belle Collaboration and confirmed as a resonance in 2014 by the LHCb collaboration. Two pentaquark states, named P+ c and P+ c, were discovered in 2015 by the LHCb collaboration, there are several more exotic hadron candidates, and other colour-singlet quark combinations may also exist. Of the hadrons, protons are stable, and neutrons bound within atomic nuclei are stable, other hadrons are unstable under ordinary conditions, free neutrons decay with a half-life of about 611 seconds. Experimentally, hadron physics is studied by colliding protons or nuclei of elements such as lead. The term hadron was introduced by Lev B, okun in a plenary talk at the 1962 International Conference on High Energy Physics. In this talk he said, Notwithstanding the fact that this report deals with weak interactions and these particles pose not only numerous scientific problems, but also a terminological problem. The point is that strongly interacting particles is a very clumsy term which does not yield itself to the formation of an adjective, for this reason, to take but one instance, decays into strongly interacting particles are called non-leptonic. This definition is not exact because non-leptonic may also signify photonic, in this report I shall call strongly interacting particles hadrons, and the corresponding decays hadronic. I hope that this terminology will prove to be convenient, okun,1962 According to the quark model, the properties of hadrons are primarily determined by their so-called valence quarks. For example, a proton is composed of two up quarks and one down quark, adding these together yields the proton charge of +1. Although quarks also carry color charge, hadrons must have total color charge because of a phenomenon called color confinement. That is, hadrons must be colorless or white and these are the simplest of the two ways, three quarks of different colors, or a quark of one color and an antiquark carrying the corresponding anticolor. Hadrons with the first arrangement are called baryons, and those with the arrangement are mesons. Hadrons, however, are not composed of just three or two quarks, because of the strength of the strong force, more accurately, strong force gluons have enough energy to have resonances composed of massive quarks. Thus, virtual quarks and antiquarks, in a 1,1 ratio, the two or three quarks that compose a hadron are the excess of quarks vs. antiquarks, and so too in the case of anti-hadrons. Massless virtual gluons compose the majority of particles inside hadrons

20.
Subatomic particle
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In the physical sciences, subatomic particles are particles much smaller than atoms. There are two types of particles, elementary particles, which according to current theories are not made of other particles. Particle physics and nuclear physics study these particles and how they interact, in particle physics, the concept of a particle is one of several concepts inherited from classical physics. But it also reflects the understanding that at the quantum scale matter. The idea of a particle underwent serious rethinking when experiments showed that light could behave like a stream of particles as well as exhibit wave-like properties and this led to the new concept of wave–particle duality to reflect that quantum-scale particles behave like both particles and waves. Another new concept, the uncertainty principle, states that some of their properties taken together, such as their simultaneous position and momentum, in more recent times, wave–particle duality has been shown to apply not only to photons but to increasingly massive particles as well. Interactions of particles in the framework of field theory are understood as creation and annihilation of quanta of corresponding fundamental interactions. This blends particle physics with field theory, any subatomic particle, like any particle in the 3-dimensional space that obeys laws of quantum mechanics, can be either a boson or a fermion. Various extensions of the Standard Model predict the existence of a graviton particle. Composite subatomic particles are bound states of two or more elementary particles, for example, a proton is made of two up quarks and one down quark, while the atomic nucleus of helium-4 is composed of two protons and two neutrons. The neutron is made of two quarks and one up quark. Composite particles include all hadrons, these include baryons and mesons, in special relativity, the energy of a particle at rest equals its mass times the speed of light squared, E = mc2. That is, mass can be expressed in terms of energy, if a particle has a frame of reference where it lies at rest, then it has a positive rest mass and is referred to as massive. Baryons tend to have greater mass than mesons, which in turn tend to be heavier than leptons and it is also certain that any particle with an electric charge is massive. These include the photon and gluon, although the latter cannot be isolated, through the work of Albert Einstein, Satyendra Nath Bose, Louis de Broglie, and many others, current scientific theory holds that all particles also have a wave nature. This has been verified not only for elementary particles but also for compound particles like atoms, interactions between particles have been scrutinized for many centuries, and a few simple laws underpin how particles behave in collisions and interactions. These are the basics of Newtonian mechanics, a series of statements and equations in Philosophiae Naturalis Principia Mathematica. The negatively charged electron has an equal to 1⁄1837 or 1836 of that of a hydrogen atom

21.
Proton
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A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and mass slightly less than that of a neutron. Protons and neutrons, each with masses of one atomic mass unit, are collectively referred to as nucleons. One or more protons are present in the nucleus of every atom, the number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number. Since each element has a number of protons, each element has its own unique atomic number. The word proton is Greek for first, and this name was given to the nucleus by Ernest Rutherford in 1920. In previous years, Rutherford had discovered that the nucleus could be extracted from the nuclei of nitrogen by atomic collisions. Protons were therefore a candidate to be a particle, and hence a building block of nitrogen. In the modern Standard Model of particle physics, protons are hadrons, and like neutrons, although protons were originally considered fundamental or elementary particles, they are now known to be composed of three valence quarks, two up quarks and one down quark. The rest masses of quarks contribute only about 1% of a protons mass, the remainder of a protons mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together. At sufficiently low temperatures, free protons will bind to electrons, however, the character of such bound protons does not change, and they remain protons. A fast proton moving through matter will slow by interactions with electrons and nuclei, the result is a protonated atom, which is a chemical compound of hydrogen. In vacuum, when electrons are present, a sufficiently slow proton may pick up a single free electron, becoming a neutral hydrogen atom. Such free hydrogen atoms tend to react chemically with other types of atoms at sufficiently low energies. When free hydrogen atoms react with other, they form neutral hydrogen molecules. Protons are spin-½ fermions and are composed of three quarks, making them baryons. Protons have an exponentially decaying positive charge distribution with a mean square radius of about 0.8 fm. Protons and neutrons are both nucleons, which may be together by the nuclear force to form atomic nuclei. The nucleus of the most common isotope of the atom is a lone proton

22.
Neutron
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The neutron is a subatomic particle, symbol n or n0, with no net electric charge and a mass slightly larger than that of a proton. Protons and neutrons, each with approximately one atomic mass unit, constitute the nucleus of an atom. Their properties and interactions are described by nuclear physics, the nucleus consists of Z protons, where Z is called the atomic number, and N neutrons, where N is the neutron number. The atomic number defines the properties of the atom. The terms isotope and nuclide are often used synonymously, but they are chemical and nuclear concepts, the atomic mass number, symbol A, equals Z+N. For example, carbon has atomic number 6, and its abundant carbon-12 isotope has 6 neutrons, some elements occur in nature with only one stable isotope, such as fluorine. Other elements occur with many stable isotopes, such as tin with ten stable isotopes, even though it is not a chemical element, the neutron is included in the table of nuclides. Within the nucleus, protons and neutrons are bound together through the nuclear force, neutrons are produced copiously in nuclear fission and fusion. They are a contributor to the nucleosynthesis of chemical elements within stars through fission, fusion. The neutron is essential to the production of nuclear power, in the decade after the neutron was discovered in 1932, neutrons were used to induce many different types of nuclear transmutations. These events and findings led to the first self-sustaining nuclear reactor, free neutrons, or individual neutrons free of the nucleus, are effectively a form of ionizing radiation, and as such, are a biological hazard, depending upon dose. A small natural background flux of free neutrons exists on Earth, caused by cosmic ray showers. Dedicated neutron sources like neutron generators, research reactors and spallation sources produce free neutrons for use in irradiation, neutrons and protons are both nucleons, which are attracted and bound together by the nuclear force to form atomic nuclei. The nucleus of the most common isotope of the atom is a lone proton. The nuclei of the hydrogen isotopes deuterium and tritium contain one proton bound to one. All other types of nuclei are composed of two or more protons and various numbers of neutrons. The most common nuclide of the chemical element lead, 208Pb has 82 protons and 126 neutrons. The free neutron has a mass of about 1. 675×10−27 kg, the neutron has a mean square radius of about 0. 8×10−15 m, or 0.8 fm, and it is a spin-½ fermion

23.
Electron
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The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, the electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the include a intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant. As it is a fermion, no two electrons can occupy the same state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of particles and waves, they can collide with other particles and can be diffracted like light. Since an electron has charge, it has an electric field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law, electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields, special telescopes can detect electron plasma in outer space. Electrons are involved in applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors. Interactions involving electrons with other particles are of interest in fields such as chemistry. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms, ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of a quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge electron in 1891, electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of isotopes and in high-energy collisions. The antiparticle of the electron is called the positron, it is identical to the electron except that it carries electrical, when an electron collides with a positron, both particles can be totally annihilated, producing gamma ray photons. The ancient Greeks noticed that amber attracted small objects when rubbed with fur, along with lightning, this phenomenon is one of humanitys earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον

24.
Neutrino
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A neutrino is a fermion that interacts only via the weak subatomic force and gravity. The mass of the neutrino is much smaller than that of the known elementary particles. The neutrino is so named because it is neutral and because its rest mass is so small that it was originally thought to be zero. The weak force has a short range, gravity is extremely weak on the subatomic scale. Thus, neutrinos pass through normal matter unimpeded and undetected. Weak interactions create neutrinos in one of three flavors, electron neutrinos, muon neutrinos, or tau neutrinos, in association with the corresponding charged lepton. Although neutrinos were long believed to be massless, it is now known there are three discrete neutrino masses with different tiny values, but they dont correspond uniquely to the three flavors. A neutrino created with a specific flavor is in a specific quantum superposition of all three mass states. Neutrinos oscillate between different flavors in flight, for example, an electron neutrino produced in a beta decay reaction may interact in a distant detector as a muon or tau neutrino. For each neutrino, there exists a corresponding antiparticle, called an antineutrino. They are distinguished from the neutrinos by having opposite signs of lepton number, the majority of neutrinos in the vicinity of the Earth are from nuclear reactions in the Sun. About 65 billion solar neutrinos per second pass through every square centimeter perpendicular to the direction of the Sun in the region of the Earth, neutrinos are also finding practical applications, such as tomography of the interior of the earth. The neutrino was postulated first by Wolfgang Pauli in 1930 to explain how beta decay could conserve energy, momentum and he considered that the new particle was emitted from the nucleus together with the electron or beta particle in the process of beta decay. James Chadwick discovered a more massive nuclear particle in 1932 and also named it a neutron. However, the journal Nature rejected Fermis paper, saying that the theory was too remote from reality. He submitted the paper to an Italian journal, which accepted it, however, by 1934 there was experimental evidence against Bohrs idea that energy conservation is invalid for beta decay. Such a limit is not expected if the conservation of energy is invalid, Pauli made use of the occasion to publicly emphasize that the still-undetected neutrino must be an actual particle. In 1942, Wang Ganchang first proposed the use of beta capture to experimentally detect neutrinos, in the 20 July 1956 issue of Science, Clyde Cowan, Frederick Reines, F. B

25.
Photon
–
A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force. The photon has zero rest mass and is moving at the speed of light. Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a photon may be refracted by a lens and exhibit wave interference with itself. The quanta in a light wave cannot be spatially localized, some defined physical parameters of a photon are listed. The modern concept of the photon was developed gradually by Albert Einstein in the early 20th century to explain experimental observations that did not fit the classical model of light. The benefit of the model was that it accounted for the frequency dependence of lights energy. The photon model accounted for observations, including the properties of black-body radiation. In that model, light was described by Maxwells equations, in 1926 the optical physicist Frithiof Wolfers and the chemist Gilbert N. Lewis coined the name photon for these particles. After Arthur H. Compton won the Nobel Prize in 1927 for his studies, most scientists accepted that light quanta have an independent existence. In the Standard Model of particle physics, photons and other particles are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of particles, such as charge, mass and it has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers, in 1900, the German physicist Max Planck was studying black-body radiation and suggested that the energy carried by electromagnetic waves could only be released in packets of energy. In his 1901 article in Annalen der Physik he called these packets energy elements, the word quanta was used before 1900 to mean particles or amounts of different quantities, including electricity. In 1905, Albert Einstein suggested that waves could only exist as discrete wave-packets. He called such a wave-packet the light quantum, the name photon derives from the Greek word for light, φῶς. Arthur Compton used photon in 1928, referring to Gilbert N. Lewis, the name was suggested initially as a unit related to the illumination of the eye and the resulting sensation of light and was used later in a physiological context. Although Wolferss and Lewiss theories were contradicted by many experiments and never accepted, in physics, a photon is usually denoted by the symbol γ

26.
Color charge
–
Color charge is a property of quarks and gluons that is related to the particles strong interactions in the theory of quantum chromodynamics. The color charge of quarks and gluons is completely unrelated to visual perception of color, another color scheme is red, yellow, and blue, using paint as the perceptible analogy. Particle physicists call these antired, antigreen, and antiblue, all three colors mixed together, or any one of these colors and its complement, is colorless or white and has a net color charge of zero. This color charge differs from electromagnetic charges since electromagnetic charges have only one kind of value, positive and negative electrical charges are the same kind of charge as they only differ by the sign. The theory of quantum chromodynamics has been under development since the 1970s, in quantum chromodynamics, a quarks color can take one of three values or charges, red, green, and blue. An antiquark can take one of three anticolors, called antired, antigreen, and antiblue, gluons are mixtures of two colors, such as red and antigreen, which constitutes their color charge. QCD considers eight gluons of the possible nine color–anticolor combinations to be unique, however, the color field lines do not arc outwards from one charge to another as much, because they are pulled together tightly by gluons. This effect confines quarks within hadrons, in a quantum field theory, a coupling constant and a charge are different but related notions. The coupling constant sets the magnitude of the force of interaction, for example, in quantum electrodynamics, the charge in a gauge theory has to do with the way a particle transforms under the gauge symmetry, i. e. its representation under the gauge group. For example, the electron has charge −1 and the positron has charge +1, since QCD is a non-abelian theory, the representations, and hence the color charges, are more complicated. They are dealt with in the next section, in QCD the gauge group is the non-abelian group SU. The running coupling is usually denoted by αs, each flavor of quark belongs to the fundamental representation and contains a triplet of fields together denoted by ψ. The antiquark field belongs to the conjugate representation and also contains a triplet of fields. We can write ψ = and ψ ¯ =, the gluon contains an octet of fields, and belongs to the adjoint representation, and can be written using the Gell-Mann matrices as A μ = A μ a λ a. All other particles belong to the representation of color SU. The color charge of each of these fields is fully specified by the representations, quarks have a color charge of red, green or blue and antiquarks have a color charge of antired, antigreen or antiblue. Gluons have a combination of two charges in a superposition of states which are given by the Gell-Mann matrices. All other particles have zero color charge, mathematically speaking, the color charge of a particle is the value of a certain quadratic Casimir operator in the representation of the particle

27.
Cosmic ray
–
Cosmic rays are high-energy radiation, mainly originating outside the Solar System. Upon impact with the Earths atmosphere, cosmic rays can produce showers of particles that sometimes reach the surface. Composed primarily of protons and atomic nuclei, they are of mysterious origin. Data from the Fermi space telescope have been interpreted as evidence that a significant fraction of cosmic rays originate from the supernovae explosions of stars. Active galactic nuclei probably also produce cosmic rays, the term ray is a historical accident, as cosmic rays were at first, and wrongly, thought to be mostly electromagnetic radiation. In current usage, the cosmic ray almost exclusively refers to massive particles. Massive particles – those that have rest mass – can gain additional, kinetic, mass-energy when they are moving, through this process, some particles acquire tremendously high mass-energies. These are significantly higher than the energy of even the highest-energy photons detected to date. The energy of the massless photon depends solely on frequency, not speed, at the higher end of the energy spectrum, relativistic kinetic energy is the main source of the mass-energy of cosmic rays. Hence, the highest-energy detected fermionic cosmic ray was around 3×106 times more energetic than the highest-energy detected cosmic photons, of primary cosmic rays, which originate outside of Earths atmosphere, about 99% are the nuclei of well-known atoms, and about 1% are solitary electrons. Of the nuclei, about 90% are simple protons, i. e. hydrogen nuclei, 9% are alpha particles, identical to helium nuclei, a very small fraction are stable particles of antimatter, such as positrons or antiprotons. The precise nature of this fraction is an area of active research. An active search from Earth orbit for anti-alpha particles has failed to detect them, one can show that such enormous energies might be achieved by means of the Centrifugal mechanism of acceleration in Active galactic nuclei. At 50 J, the highest-energy ultra-high-energy cosmic rays have energies comparable to the energy of a 90-kilometre-per-hour baseball. As a result of discoveries, there has been interest in investigating cosmic rays of even greater energies. Most cosmic rays, however, do not have such extreme energies, however, his paper published in Physikalische Zeitschrift was not widely accepted. In 1911 Domenico Pacini observed simultaneous variations of the rate of ionization over a lake, over the sea, Pacini concluded from the decrease of radioactivity underwater that a certain part of the ionization must be due to sources other than the radioactivity of the Earth. In 1912, Victor Hess carried three enhanced-accuracy Wulf electrometers to an altitude of 5300 meters in a balloon flight

28.
Antiproton
–
The antiproton, p, is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived, since any collision with a proton will cause particles to be annihilated in a burst of energy. The existence of the antiproton with −1 electric charge, opposite to the +1 electric charge of the proton, was predicted by Paul Dirac in his 1933 Nobel Prize lecture, in terms of valence quarks, an antiproton consists of two up antiquarks and one down antiquark. Antiprotons have been detected in cosmic rays for over 25 years, first by balloon-borne experiments and their energy spectrum is modified by collisions with other atoms in the interstellar medium, and antiprotons can also be lost by leaking out of the galaxy. The antiproton cosmic ray energy spectrum is now measured reliably and is consistent with this picture of antiproton production by cosmic ray collisions. This also provides a limit on the antiproton lifetime of about 1-10 million years. Since the galactic storage time of antiprotons is about 10 million years and this is significantly more stringent than the best laboratory measurements of the antiproton lifetime, LEAR collaboration at CERN,0.08 years Antihydrogen Penning trap of Gabrielse et al. CPT symmetry is a consequence of quantum field theory and no violations of it have ever been detected. BESS, balloon-borne experiment, flown in 1993,1995,1997,2000,2002,2004 and 2007, CAPRICE, balloon-borne experiment, flown in 1994 and 1998. HEAT, balloon-borne experiment, flown in 2000, AMS, space-based experiment, prototype flown on the space shuttle in 1998, intended for the International Space Station, launched May 2011. PAMELA, satellite experiment to detect cosmic rays and antimatter from space, recent report discovered 28 antiprotons in the South Atlantic Anomaly. Antiprotons are routinely produced at Fermilab for collider physics operations in the Tevatron, the use of antiprotons allows for a higher average energy of collisions between quarks and antiquarks than would be possible in proton-proton collisions. This is because the valence quarks in the proton, and the valence antiquarks in the antiproton and their formation requires energy equivalent to a temperature of 10 trillion K and this does not tend to happen naturally. However, at CERN, protons are accelerated in the Proton Synchrotron to an energy of 26 GeV, the protons bounce off the iridium nuclei with enough energy for matter to be created. A range of particles and antiparticles are formed, and the antiprotons are separated off using magnets in vacuum, in July 2011, the ASACUSA experiment at CERN determined the mass of the antiproton to be 1836.1526736 times more massive than an electron. This is the same as the mass of a proton, within the level of certainty of the experiment, antiprotons have been shown within laboratory experiments to have the potential to treat certain cancers, in a similar method currently used for ion therapy. The primary difference between therapy and proton therapy is that following ion energy deposition the antiproton annihilates depositing additional energy in the cancerous region. Antimatter Antineutron Positron Antihydrogen Antiprotonic helium List of particles Recycling antimatter

29.
Nuclear force
–
The nuclear force is a force that acts between the protons and neutrons of atoms. Neutrons and protons, both nucleons, are affected by the force almost identically. The nuclear force binds nucleons into atomic nuclei, the nuclear force is powerfully attractive between nucleons at distances of about 1 femtometer, but it rapidly decreases to insignificance at distances beyond about 2.5 fm. At distances less than 0.7 fm, the force becomes repulsive. This repulsive component is responsible for the size of nuclei. By comparison, the size of an atom, measured in angstroms, is five orders of magnitude larger. The nuclear force is not simple, however, since it depends on the spins, has a tensor component. The nuclear force is not one of the forces of nature. The nuclear force plays an role in storing energy that is used in nuclear power. Work is required to bring charged protons together against their electric repulsion and this energy is stored when the protons and neutrons are bound together by the nuclear force to form a nucleus. The mass of a nucleus is less than the sum total of the masses of the protons and neutrons. The difference in masses is known as the defect, which can be expressed as an energy equivalent. Energy is released when a heavy nucleus breaks apart into two or more lighter nuclei and this energy is the electromagnetic potential energy that is released when the nuclear force no longer holds the charged nuclear fragments together. A quantitative description of the nuclear force relies on equations that are partly empirical and these equations model the internucleon potential energies, or potentials. The constants for the equations are phenomenological, that is, determined by fitting the equations to experimental data, the internucleon potentials attempt to describe the properties of nucleon–nucleon interaction. Once determined, any potential can be used in, e. g. the Schrödinger equation to determine the quantum mechanical properties of the nucleon system. The discovery of the neutron in 1932 revealed that atomic nuclei were made of protons and neutrons, by 1935 the nuclear force was conceived to be transmitted by particles called mesons. This theoretical development included a description of the Yukawa potential, an example of a nuclear potential

30.
Big Bang
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The Big Bang theory is the prevailing cosmological model for the universe from the earliest known periods through its subsequent large-scale evolution. If the known laws of physics are extrapolated to the highest density regime, detailed measurements of the expansion rate of the universe place this moment at approximately 13.8 billion years ago, which is thus considered the age of the universe. After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, giant clouds of these primordial elements later coalesced through gravity in halos of dark matter, eventually forming the stars and galaxies visible today. Since Georges Lemaître first noted in 1927 that a universe could be traced back in time to an originating single point. More recently, measurements of the redshifts of supernovae indicate that the expansion of the universe is accelerating, the known physical laws of nature can be used to calculate the characteristics of the universe in detail back in time to an initial state of extreme density and temperature. American astronomer Edwin Hubble observed that the distances to faraway galaxies were strongly correlated with their redshifts, assuming the Copernican principle, the only remaining interpretation is that all observable regions of the universe are receding from all others. Since we know that the distance between galaxies increases today, it must mean that in the past galaxies were closer together, the continuous expansion of the universe implies that the universe was denser and hotter in the past. Large particle accelerators can replicate the conditions that prevailed after the early moments of the universe, resulting in confirmation, however, these accelerators can only probe so far into high energy regimes. Consequently, the state of the universe in the earliest instants of the Big Bang expansion is still poorly understood, the first subatomic particles to be formed included protons, neutrons, and electrons. Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed before the first electrically neutral atoms formed, the majority of atoms produced by the Big Bang were hydrogen, along with helium and traces of lithium. Giant clouds of primordial elements later coalesced through gravity to form stars and galaxies. The framework for the Big Bang model relies on Albert Einsteins theory of relativity and on simplifying assumptions such as homogeneity. The governing equations were formulated by Alexander Friedmann, and similar solutions were worked on by Willem de Sitter, extrapolation of the expansion of the universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past. This singularity indicates that general relativity is not a description of the laws of physics in this regime. How closely models based on general relativity alone can be used to extrapolate toward the singularity is debated—certainly no closer than the end of the Planck epoch. This primordial singularity is itself called the Big Bang, but the term can also refer to a more generic early hot. The agreement of independent measurements of this age supports the model that describes in detail the characteristics of the universe. The earliest phases of the Big Bang are subject to much speculation, in the most common models the universe was filled homogeneously and isotropically with a very high energy density and huge temperatures and pressures and was very rapidly expanding and cooling

31.
Particle accelerator
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A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to nearly light speed and to contain them in well-defined beams. Large accelerators are used in physics as colliders, or as synchrotron light sources for the study of condensed matter physics. There are currently more than 30,000 accelerators in operation around the world, there are two basic classes of accelerators, electrostatic and electrodynamic accelerators. Electrostatic accelerators use electric fields to accelerate particles. The most common types are the Cockcroft–Walton generator and the Van de Graaff generator, a small-scale example of this class is the cathode ray tube in an ordinary old television set. The achievable kinetic energy for particles in these devices is determined by the accelerating voltage, electrodynamic or electromagnetic accelerators, on the other hand, use changing electromagnetic fields to accelerate particles. Since in these types the particles can pass through the accelerating field multiple times. This class, which was first developed in the 1920s, is the basis for most modern large-scale accelerators, because colliders can give evidence of the structure of the subatomic world, accelerators were commonly referred to as atom smashers in the 20th century. Despite the fact that most accelerators actually propel subatomic particles, the term persists in popular usage when referring to particle accelerators in general. Beams of high-energy particles are useful for both fundamental and applied research in the sciences, and also in many technical and industrial fields unrelated to fundamental research and it has been estimated that there are approximately 30,000 accelerators worldwide. The bar graph shows the breakdown of the number of industrial accelerators according to their applications, for the most basic inquiries into the dynamics and structure of matter, space, and time, physicists seek the simplest kinds of interactions at the highest possible energies. These typically entail particle energies of many GeV, and the interactions of the simplest kinds of particles, leptons and quarks for the matter, the largest and highest energy particle accelerator used for elementary particle physics is the Large Hadron Collider at CERN, operating since 2009. These investigations often involve collisions of heavy nuclei – of atoms like iron or gold – at energies of several GeV per nucleon, the largest such particle accelerator is the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. An example of type of machine is LANSCE at Los Alamos. A large number of light sources exist worldwide. The ESRF in Grenoble, France has been used to extract detailed 3-dimensional images of trapped in amber. Thus there is a demand for electron accelerators of moderate energy. Everyday examples of particle accelerators are cathode ray tubes found in television sets and these low-energy accelerators use a single pair of electrodes with a DC voltage of a few thousand volts between them

32.
Baryon
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A baryon is a composite subatomic particle made up of three quarks. Baryons and mesons belong to the family of particles, which are the quark-based particles. The name baryon comes from the Greek word for heavy, because, at the time of their naming, as quark-based particles, baryons participate in the strong interaction, whereas leptons, which are not quark-based, do not. The most familiar baryons are the protons and neutrons that make up most of the mass of the matter in the universe. Each baryon has a corresponding antiparticle where quarks are replaced by their corresponding antiquarks, for example, a proton is made of two up quarks and one down quark, and its corresponding antiparticle, the antiproton, is made of two up antiquarks and one down antiquark. This is in contrast to the bosons, which do not obey the exclusion principle, Baryons, along with mesons, are hadrons, meaning they are particles composed of quarks. Quarks have baryon numbers of B = 1/3 and antiquarks have baryon number of B = −1/3, the term baryon usually refers to triquarks—baryons made of three quarks. Other exotic baryons have been proposed, such as made of four quarks and one antiquark. The particle physics community as a whole did not view their existence as likely in 2006, however, in July 2015, the LHCb experiment observed two resonances consistent with pentaquark states in the Λ0 b → J/ψK−p decay, with a combined statistical significance of 15σ. In theory, heptaquarks, nonaquarks, etc. could also exist, nearly all matter that may be encountered or experienced in everyday life is baryonic matter, which includes atoms of any sort, and provides those with the property of mass. Non-baryonic matter, as implied by the name, is any sort of matter that is not composed primarily of baryons and this might include neutrinos and free electrons, dark matter, such as supersymmetric particles, axions, and black holes. The very existence of baryons is also a significant issue in cosmology, the process by which baryons came to outnumber their antiparticles is called baryogenesis. Some grand unified theories of physics also predict that a single proton can decay, changing the baryon number by one, however. The excess of baryons over antibaryons in the present universe is thought to be due to non-conservation of baryon number in the early universe. The concept of isospin was first proposed by Werner Heisenberg in 1932 to explain the similarities between protons and neutrons under the strong interaction, although they had different electric charges, their masses were so similar that physicists believed they were the same particle. The different electric charges were explained as being the result of some unknown excitation similar to spin and this unknown excitation was later dubbed isospin by Eugene Wigner in 1937. This belief lasted until Murray Gell-Mann proposed the model in 1964. The success of the model is now understood to be the result of the similar masses of the u and d quarks

33.
Exotic meson
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All of these can be classed as mesons, because they are hadrons and carry zero baryon number. Of these, glueballs must be flavor singlets, that is, have zero isospin, strangeness, charm, bottomness, like all particle states, they are specified by the quantum numbers which label representations of the Poincaré symmetry, q. e. One also specifies the isospin I of the meson, typically, every quark model meson comes in SU flavor nonet, an octet and a flavor singlet. A glueball shows up as a particle outside the nonet. In spite of seemingly simple counting, the assignment of any given state as a glueball, tetraquark. Even when there is agreement that one of states is one of these non-quark model mesons, the degree of mixing. There is also the considerable labor of assigning quantum numbers to each state. As a result, all assignments outside the model are tentative. The remainder of this article outlines the situation as it stood at the end of 2004, lattice QCD predictions for glueballs are now fairly stable, at least when virtual quarks are neglected. The two lowest states are 0++ with mass of 1611±163 MeV/c2 and 2++ with mass of 2232±310 MeV/c2 The 0−+, glueballs are necessarily isoscalar, with isospin I =0. The ground state hybrid mesons 0−+, 1−+, 1−−, the hybrid with exotic quantum numbers 1−+ is at 1. 9±0.2 GeV/c2. The best lattice computations to date are made in the quenched approximation, as a result, these computations miss mixing with meson states. The data show five isoscalar resonances, f0, f0, f0, f0, of these the f0 is usually identified with the σ of chiral models. The decays and production of f0 give strong evidence that it is also a meson, the f0 and f0 cannot both be a quark model meson, because one is supernumerary. The production of the mass state in two photon reactions such as 2γ → 2π or 2γ → 2K reactions is highly suppressed. The decays also give evidence that one of these could be a glueball. The f0 has been identified by some authors as a meson, along with the I =1 states a0. Two long-lived states, the scalar state D*± sJ and the vector meson D*± sJ, observed at CLEO, however, for these, other explanations are possible

34.
Fermion
–
In particle physics, a fermion is any subatomic particle characterized by Fermi–Dirac statistics. These particles obey the Pauli exclusion principle, fermions include all quarks and leptons, as well as any composite particle made of an odd number of these, such as all baryons and many atoms and nuclei. Fermions differ from bosons, which obey Bose–Einstein statistics, a fermion can be an elementary particle, such as the electron, or it can be a composite particle, such as the proton. According to the theorem in any reasonable relativistic quantum field theory, particles with integer spin are bosons. Besides this spin characteristic, fermions have another specific property, they possess conserved baryon or lepton quantum numbers, therefore, what is usually referred to as the spin statistics relation is in fact a spin statistics-quantum number relation. As a consequence of the Pauli exclusion principle, only one fermion can occupy a quantum state at any given time. If multiple fermions have the same probability distribution, then at least one property of each fermion, such as its spin. Weakly interacting fermions can also display bosonic behavior under extreme conditions, at low temperature fermions show superfluidity for uncharged particles and superconductivity for charged particles. Composite fermions, such as protons and neutrons, are the key building blocks of everyday matter, the Standard Model recognizes two types of elementary fermions, quarks and leptons. In all, the model distinguishes 24 different fermions, there are six quarks, and six leptons, along with the corresponding antiparticle of each of these. Mathematically, fermions come in three types - Weyl fermions, Dirac fermions, and Majorana fermions, most Standard Model fermions are believed to be Dirac fermions, although it is unknown at this time whether the neutrinos are Dirac or Majorana fermions. Dirac fermions can be treated as a combination of two Weyl fermions, in July 2015, Weyl fermions have been experimentally realized in Weyl semimetals. Composite particles can be bosons or fermions depending on their constituents, more precisely, because of the relation between spin and statistics, a particle containing an odd number of fermions is itself a fermion. Examples include the following, A baryon, such as the proton or neutron, the nucleus of a carbon-13 atom contains six protons and seven neutrons and is therefore a fermion. The atom helium-3 is made of two protons, one neutron, and two electrons, and therefore it is a fermion. The number of bosons within a composite made up of simple particles bound with a potential has no effect on whether it is a boson or a fermion. Fermionic or bosonic behavior of a particle is only seen at large distances. At proximity, where spatial structure begins to be important, a composite particle behaves according to its constituent makeup, fermions can exhibit bosonic behavior when they become loosely bound in pairs

35.
Parity (physics)
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In quantum mechanics, a parity transformation is the flip in the sign of one spatial coordinate. In three dimensions, it is often described by the simultaneous flip in the sign of all three spatial coordinates, P, ↦. It can also be thought of as a test for chirality of a physical phenomenon, a parity transformation on something achiral, on the other hand, can be viewed as an identity transformation. All fundamental interactions of particles, with the exception of the weak interaction, are symmetric under parity. The weak interaction is chiral and thus provides a means for probing chirality in physics, in interactions that are symmetric under parity, such as electromagnetism in atomic and molecular physics, parity serves as a powerful controlling principle underlying quantum transitions. A matrix representation of P has determinant equal to −1, and hence is distinct from a rotation, in a two-dimensional plane, a simultaneous flip of all coordinates in sign is not a parity transformation, it is the same as a 180°-rotation. Under rotations, classical geometrical objects can be classified into scalars, vectors, in classical physics, physical configurations need to transform under representations of every symmetry group. Quantum theory predicts that states in a Hilbert space do not need to transform under representations of the group of rotations, the projective representations of any group are isomorphic to the ordinary representations of a central extension of the group. For example, projective representations of the 3-dimensional rotation group, which is the orthogonal group SO, are ordinary representations of the special unitary group SU. Projective representations of the group that are not representations are called spinors. If one adds to this a classification by parity, these can be extended, for example, vectors and axial vectors which both transform as vectors under rotation. One can define reflections such as V x, ↦, which also have negative determinant, then, combining them with rotations one can recover the particular parity transformation defined earlier. The first parity transformation given does not work in an number of dimensions, though. In odd number of only the latter example of a parity transformation can be used. Parity forms the abelian group Z2 due to the relation P2 =1, all Abelian groups have only one-dimensional irreducible representations. For Z2, there are two representations, one is even under parity, the other is odd. These are useful in quantum mechanics, newtons equation of motion F = ma equates two vectors, and hence is invariant under parity. The law of gravity also involves only vectors and is also, therefore, however, angular momentum L is an axial vector, L = r × p, P = × = L

36.
Mass
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In physics, mass is a property of a physical body. It is the measure of a resistance to acceleration when a net force is applied. It also determines the strength of its gravitational attraction to other bodies. The basic SI unit of mass is the kilogram, Mass is not the same as weight, even though mass is often determined by measuring the objects weight using a spring scale, rather than comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity and this is because weight is a force, while mass is the property that determines the strength of this force. In Newtonian physics, mass can be generalized as the amount of matter in an object, however, at very high speeds, special relativity postulates that energy is an additional source of mass. Thus, any body having mass has an equivalent amount of energy. In addition, matter is a defined term in science. There are several distinct phenomena which can be used to measure mass, active gravitational mass measures the gravitational force exerted by an object. Passive gravitational mass measures the force exerted on an object in a known gravitational field. The mass of an object determines its acceleration in the presence of an applied force, according to Newtons second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. A bodys mass also determines the degree to which it generates or is affected by a gravitational field and this is sometimes referred to as gravitational mass. The standard International System of Units unit of mass is the kilogram, the kilogram is 1000 grams, first defined in 1795 as one cubic decimeter of water at the melting point of ice. Then in 1889, the kilogram was redefined as the mass of the prototype kilogram. As of January 2013, there are proposals for redefining the kilogram yet again. In this context, the mass has units of eV/c2, the electronvolt and its multiples, such as the MeV, are commonly used in particle physics. The atomic mass unit is 1/12 of the mass of a carbon-12 atom, the atomic mass unit is convenient for expressing the masses of atoms and molecules. Outside the SI system, other units of mass include, the slug is an Imperial unit of mass, the pound is a unit of both mass and force, used mainly in the United States

37.
Atomic nucleus
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After the discovery of the neutron in 1932, models for a nucleus composed of protons and neutrons were quickly developed by Dmitri Ivanenko and Werner Heisenberg. Almost all of the mass of an atom is located in the nucleus, protons and neutrons are bound together to form a nucleus by the nuclear force. The diameter of the nucleus is in the range of 6985175000000000000♠1.75 fm for hydrogen to about 6986150000000000000♠15 fm for the heaviest atoms and these dimensions are much smaller than the diameter of the atom itself, by a factor of about 23,000 to about 145,000. The branch of physics concerned with the study and understanding of the nucleus, including its composition. The nucleus was discovered in 1911, as a result of Ernest Rutherfords efforts to test Thomsons plum pudding model of the atom, the electron had already been discovered earlier by J. J. Knowing that atoms are electrically neutral, Thomson postulated that there must be a charge as well. In his plum pudding model, Thomson suggested that an atom consisted of negative electrons randomly scattered within a sphere of positive charge, to his surprise, many of the particles were deflected at very large angles. This justified the idea of an atom with a dense center of positive charge. The term nucleus is from the Latin word nucleus, a diminutive of nux, in 1844, Michael Faraday used the term to refer to the central point of an atom. The modern atomic meaning was proposed by Ernest Rutherford in 1912, the adoption of the term nucleus to atomic theory, however, was not immediate. In 1916, for example, Gilbert N, the nuclear strong force extends far enough from each baryon so as to bind the neutrons and protons together against the repulsive electrical force between the positively charged protons. The nuclear strong force has a short range, and essentially drops to zero just beyond the edge of the nucleus. The collective action of the charged nucleus is to hold the electrically negative charged electrons in their orbits about the nucleus. The collection of negatively charged electrons orbiting the nucleus display an affinity for certain configurations, which chemical element an atom represents is determined by the number of protons in the nucleus, the neutral atom will have an equal number of electrons orbiting that nucleus. Individual chemical elements can create more stable electron configurations by combining to share their electrons and it is that sharing of electrons to create stable electronic orbits about the nucleus that appears to us as the chemistry of our macro world. Protons define the entire charge of a nucleus, and hence its chemical identity, neutrons are electrically neutral, but contribute to the mass of a nucleus to nearly the same extent as the protons. Neutrons explain the phenomenon of isotopes – varieties of the chemical element which differ only in their atomic mass. They are sometimes viewed as two different quantum states of the particle, the nucleon

38.
Ancient Greek
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Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Aeolic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are also several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the later Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians, Aeolians, and Ionians, each with their own defining and distinctive dialects. Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek

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Werner Heisenberg
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Werner Karl Heisenberg was a German theoretical physicist and one of the key pioneers of quantum mechanics. He published his work in 1925 in a breakthrough paper, in the subsequent series of papers with Max Born and Pascual Jordan, during the same year, this matrix formulation of quantum mechanics was substantially elaborated. In 1927 he published his uncertainty principle, upon which he built his philosophy, Heisenberg was awarded the Nobel Prize in Physics for 1932 for the creation of quantum mechanics. He was a principal scientist in the Nazi German nuclear weapon project during World War II and he travelled to occupied Copenhagen where he met and discussed the German project with Niels Bohr. Following World War II, he was appointed director of the Kaiser Wilhelm Institute for Physics and he was director of the institute until it was moved to Munich in 1958, when it was expanded and renamed the Max Planck Institute for Physics and Astrophysics. He studied physics and mathematics from 1920 to 1923 at the Ludwig-Maximilians-Universität München, at Munich, he studied under Arnold Sommerfeld and Wilhelm Wien. At Göttingen, he studied physics with Max Born and James Franck and he received his doctorate in 1923, at Munich under Sommerfeld. He completed his Habilitation in 1924, at Göttingen under Born, at the event, Bohr was a guest lecturer and gave a series of comprehensive lectures on quantum atomic physics. There, Heisenberg met Bohr for the first time, and it had a significant, Heisenbergs doctoral thesis, the topic of which was suggested by Sommerfeld, was on turbulence, the thesis discussed both the stability of laminar flow and the nature of turbulent flow. The problem of stability was investigated by the use of the Orr–Sommerfeld equation and he briefly returned to this topic after World War II. Heisenbergs paper on the anomalous Zeeman effect was accepted as his Habilitationsschrift under Max Born at Göttingen, in his youth he was a member and Scoutleader of the Neupfadfinder, a German Scout association and part of the German Youth Movement. In August 1923 Robert Honsell and Heisenberg organized a trip to Finland with a Scout group of this association from Munich, Heisenberg arrived at Munich in 1919 as a member of Freikorps to fight the Bavarian Soviet Republic established a year earlier. Five decades later he recalled those days as youthful fun, like playing cops and robbers and so on, from 1924 to 1927, Heisenberg was a Privatdozent at Göttingen. His seminal paper, Über quantentheoretischer Umdeutung was published in September 1925 and he returned to Göttingen and with Max Born and Pascual Jordan, over a period of about six months, developed the matrix mechanics formulation of quantum mechanics. On 1 May 1926, Heisenberg began his appointment as a university lecturer and it was in Copenhagen, in 1927, that Heisenberg developed his uncertainty principle, while working on the mathematical foundations of quantum mechanics. On 23 February, Heisenberg wrote a letter to fellow physicist Wolfgang Pauli, in his paper on the uncertainty principle, Heisenberg used the word Ungenauigkeit. In 1927, Heisenberg was appointed ordentlicher Professor of theoretical physics and head of the department of physics at the Universität Leipzig, in his first paper published from Leipzig, Heisenberg used the Pauli exclusion principle to solve the mystery of ferromagnetism. Slater, Edward Teller, John Hasbrouck van Vleck, Victor Frederick Weisskopf, Carl Friedrich von Weizsäcker, Gregor Wentzel, in early 1929, Heisenberg and Pauli submitted the first of two papers laying the foundation for relativistic quantum field theory

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Ludwig Maximilian University of Munich
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Ludwig-Maximilians-Universität in Munich is a public research university located in Munich, Germany. The University of Munich is among Germanys oldest universities, in 1802, the university was officially named Ludwig-Maximilians-Universität by King Maximilian I of Bavaria in his as well as the universitys original founders honour. Among these were Wilhelm Röntgen, Max Planck, Werner Heisenberg, Otto Hahn, pope Benedict XVI was also a student and professor at the university. The LMU has recently been conferred the title of university under the German Universities Excellence Initiative. LMU is currently the second-largest university in Germany in terms of student population, in the semester of 2015/2016. Of these,8,671 were freshmen while international students totalled 7,812 or almost 15% of the student population, the university was founded with papal approval in 1472 as the University of Ingolstadt, with faculties of philosophy, medicine, jurisprudence and theology. Its first rector was Christopher Mendel of Steinfels, who became bishop of Chiemsee. In the period of German humanism, the universitys academics included names such as Conrad Celtes, the theologian Johann Eck also taught at the university. From 1549 to 1773, the university was influenced by the Jesuits, the Jesuit Petrus Canisius served as rector of the university. At the end of the 18th century, the university was influenced by the Enlightenment, in 1800, the Prince-Elector Maximilianv IV Joseph moved the university to Landshut, due to French aggression that threatened Ingolstadt during the Napoleonic Wars. In 1802, the university was renamed the Ludwig Maximilian University in honour of its two founders, Louis IX, Duke of Bavaria and Maximilian I, Elector of Bavaria. The Minister of Education, Maximilian von Montgelas, initiated a number of reforms sought to modernize the rather conservative. In 1826, it was moved to Munich, the capital of the Kingdom of Bavaria, the university was situated in the Old Academy until a new building in the Ludwigstraße was completed. The locals were critical of the number of Protestant professors Maximilian. They were dubbed the Nordlichter and especially physician Johann Nepomuk von Ringseis was quite angry about them, in the second half of the 19th century, the university rose to great prominence in the European scientific community, attracting many of the worlds leading scientists. It was also a period of great expansion, from 1903, women were allowed to study at Bavarian universities, and by 1918, the female proportion of students at LMU had reached 18%. In 1918, Adele Hartmann became the first woman in Germany to earn the Habilitation, during the Third Reich, academic freedom was severely curtailed. In 1943 the White Rose group of anti-Nazi students conducted their campaign of opposition to the National Socialists at this university, the university has continued to be one of the leading universities of West Germany during the Cold War and in the post-reunification era

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Muon
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The muon is an elementary particle similar to the electron, with an electric charge of −1 e and a spin of 1/2, but with a much greater mass. It is classified as a lepton, as is the case with other leptons, the muon is not believed to have any sub-structure—that is, it is not thought to be composed of any simpler particles. The muon is a subatomic particle with a mean lifetime of 2.2 µs. Muon decay almost always produces at least three particles, which must include an electron of the charge as the muon and two neutrinos of different types. Like all elementary particles, the muon has a corresponding antiparticle of opposite charge but equal mass and spin, muons are denoted by μ− and antimuons by μ+. Muons were previously called mu mesons, but are not classified as mesons by modern particle physicists, muons have a mass of 105.7 MeV/c2, which is about 207 times that of the electron. Due to their mass, muons are not as sharply accelerated when they encounter electromagnetic fields. As an example, so-called secondary muons, generated by cosmic rays hitting the atmosphere, can penetrate to the Earths surface, because muons have a very large mass and energy compared with the decay energy of radioactivity, they are never produced by radioactive decay. These interactions usually produce pi mesons initially, which most often decay to muons, muons were discovered by Carl D. Anderson and Seth Neddermeyer at Caltech in 1936, while studying cosmic radiation. Anderson noticed particles that curved differently from electrons and other known particles when passed through a magnetic field and they were negatively charged but curved less sharply than electrons, but more sharply than protons, for particles of the same velocity. Thus Anderson initially called the new particle a mesotron, adopting the prefix meso- from the Greek word for mid-, the existence of the muon was confirmed in 1937 by J. C. The transition of a particle from neutron state to proton state is not always accompanied by the emission of light particles. The transition is taken up by another heavy particle. Because of its mass, the mu meson was initially thought to be Yukawas particle, with two particles now known with the intermediate mass, the more general term meson was adopted to refer to any such particle within the correct mass range between electrons and nucleons. The difference, in part, was that mu mesons did not interact with the nuclear force, newer mesons also showed evidence of behaving like the pi meson in nuclear interactions, but not like the mu meson. Also, the mu mesons decay products included both a neutrino and an antineutrino, rather than just one or the other, as was observed in the decay of other charged mesons. In the quark model, a meson was no longer defined by mass, mu mesons, however, had shown themselves to be fundamental particles like electrons, with no quark structure. Thus, mu mesons were not mesons at all, in the new sense and use of the term used with the quark model of particle structure

Two-dimensional analogy of spacetime distortion generated by the mass of an object. Matter changes the geometry of spacetime, this (curved) geometry being interpreted as gravity. White lines do not represent the curvature of space but instead represent the coordinate system imposed on the curved spacetime, which would be rectilinear in a flat spacetime.

An initially-stationary object which is allowed to fall freely under gravity drops a distance which is proportional to the square of the elapsed time. This image spans half a second and was captured at 20 flashes per second.

The Big Bang theory is the prevailing cosmological model for the universe from the earliest known periods through its …

Timeline of the metric expansion of space, where space (including hypothetical non-observable portions of the universe) is represented at each time by the circular sections. On the left, the dramatic expansion occurs in the inflationary epoch; and at the center, the expansion accelerates (artist's concept; not to scale).

Panoramic view of the entire near-infrared sky reveals the distribution of galaxies beyond the Milky Way. Galaxies are color-coded by redshift.

Artist's depiction of the WMAP satellite gathering data to help scientists understand the Big Bang

Cold neutron source providing neutrons at about the temperature of liquid hydrogen

Models depicting the nucleus and electron energy levels in hydrogen, helium, lithium, and neon atoms. In reality, the diameter of the nucleus is about 100,000 times smaller than the diameter of the atom.

Nuclear fission caused by absorption of a neutron by uranium-235. The heavy nuclide fragments into lighter components and additional neutrons.

The nuclear force (or nucleon–nucleon interaction or residual strong force) is a force that acts between the protons …

Image: Reid Force 2

Corresponding potential energy (in units of MeV) of two nucleons as a function of distance as computed from the Reid potential. The potential well is a minimum at a distance of about 0.8 fm. With this potential nucleons can become bound with a negative "binding energy."

In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary …

Schematic diagram depicting the spin of the neutron as the black arrow and magnetic field lines associated with the neutron magnetic moment. The neutron has a negative magnetic moment. While the spin of the neutron is upward in this diagram, the magnetic field lines at the center of the dipole are downward.

A photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation …

The Wave–particle duality of light best explains the particle quanta and wave properties present in light, composed of photons representing the energy imparted by an electromagnetic wave.

In this illustration, one photon (purple) carries a million times the energy of another (yellow). Credit: NASA/Sonoma State University/Aurore Simonnet

Stimulated emission (in which photons "clone" themselves) was predicted by Einstein in his kinetic analysis, and led to the development of the laser. Einstein's derivation inspired further developments in the quantum treatment of light, which led to the statistical interpretation of quantum mechanics.

Diagram showing field lines and equipotentials around an electron, a negatively charged particle. In an electrically neutral atom, the number of electrons is equal to the number of protons (which are positively charged), resulting in a net zero overall charge

Electric field induced by a positive electric charge (left) and a field induced by a negative electric charge (right).